1. Field of the Invention
This invention relates generally to a bicycle freewheel which is used to transmit only a forward driving force while allowing idle or inertial running of the bicycle. More specifically, the invention relates to a multiple freewheel for a bicycle which includes a set of diametrically different sprockets to further enable speed selection.
2. Description of the Prior Art
As is well known, the bicycle freewheel is generally mounted to the rear hub of the bicycle to constitute a rear gear which is connected via the chain to the chainwheel constituting a front gear. Forward pedalling causes the front gear and thereby the freewheel to drivingly rotate with the rear hub, consequently driving the bicycle forward. On the other hand, the freewheel allows forward rotation of rear hub in the absence of forward pedalling to enable idle forward running of the bicycle.
A typical multiple freewheel for a bicycle comprises an inner ring fixed to one side of the bicycle rear hub, an outer sprocket ring or carrier rotatably supported on the inner ring via a one-way clutch, and a set of diametrically different sprockets fitted axially onto the sprocket ring. Each sprocket has a central opening formed with engaging projections for engagement with axially extending spline grooves formed on the outer surface of the sprocket ring, so that the sprocket set co-rotates with the sprocket ring. The chain connected to the front gear engages with a selected sprocket of the freewheel but may be shifted to another selected sprocket to effect a speed change.
In assembly of the multiple freewheel, the individual sprockets must be separately fitted in succession onto the sprocket ring with their engaging projections aligned with the spline grooves of the sprocket ring. In so doing, further, spacer rings must also be fitted onto the sprocket ring to ensure suitable spacing between each two adjacent sprockets. Finally, a nut member is screwed on the sprocket ring to prevent axial displacement of the assembled set of sprockets and spacer rings. Therefore, such an assembling operation is unavoidably time-taking.
With a view to facilitating assembly, Japanese Utility Model Publication No. 55-23017 (Published: May 31, 1980; Applicant: Shimano Industrial Company; Inventors: Masashi NAGANO et al) discloses a multiple freewheel for a bicycle which incorporates a preassembled set of diametrically different sprockets to be axially fitted onto a sprocket ring or carrier. More specifically, each of the sprockets has preassembly holes at corresponding positions, and a bolt having an head in abutment with the largest sprocket is inserted through a corresponding preassembly hole of each sprocket to project out of the smallest sprocket. The projecting end of the bolt is threaded to engage in a nut which, when screwably advanced, comes into abutment with the smallest sprocket, thereby clamping the set of sprockets between the bolt head and the nut in a preassembled condition. After mounting of the preassembled set of sprockets onto the sprocket carrier, a stopper ring is fitted on the sprocket carrier to prevent axial displacement of the sprocket set.
With the preassembly type freewheel of the above Japanese publication, the set of sprockets are maintained in the preassembled condition even after mounting thereof onto the sprocket carrier. In other words, the individual sprockets have no independency once they are preassembled. This gives rise to a problem in replacing only one of the sprockets after complete assembly. In fact, it is needed to remove the entire set of sprockets before replacing a selected sprocket. Such a disadvantage becomes more significant particularly when only the smallest sprocket, which is located at a position for easiest access from outside, need be replaced.